Such cylinders are often designed for single-fill use and may be obliged by governmental regulation to have a device which prevents them from being refilled.
Various refill prevention devices are known which employ, e.g., the principle of triggering. In these devices, the cylinder is filled with gas and then a trigger is activated that releases a check valve mechanism within the valve. Such devices require those performing the filling operation to know before filling the cylinder that the operation of a refill prevention device is needed. Such a device is the subject of U.S. Pat. No. 5,018,552.
In such known devices, the check valve mechanism is continuously exposed to the gas within the cylinder and so there is the danger that the gas can interact with parts of the check valve.
Another refill prevention device is of the type of U.S. Pat. Nos. 3,552,432 and 3,589,397. In each of these, a handle can be screwed into and out of a housing so as to control the flow of gas through the housing. When the handle is in its farthest outward position, a container to which the housing is secured can be filled. In its farthest inward position, the handle closes the container; and in an intermediate position to which the handle can be backed off, the pressurized contents of the container can be dispensed. After filling, a portion of the housing is crimped to prevent retrograde movement of the handle beyond that intermediate position, so that the handle can no longer be withdrawn to the point that the container can be refilled.
A somewhat similar device is disclosed in U.S. Pat. No. 3,985,332, in which a hollow knob has three similar positions, namely, an outermost position in which the container can be filled, an innermost position in which the container is closed, and an intermediate position in which gas under pressure can be dispensed from the container. Upon the completion of filling and the movement of the hollow knob to the innermost position, an outwardly biassed spring snaps outwardly to prevent retrograde movement of the handle outwardly beyond the intermediate position.
In French Patent 2 634 852, a frangible rod holds a valve member withdrawn until after filling. Once the container is filled, the rod is ruptured and the valve member thereafter closes the container or permits gas to be withdrawn from the container, but does not permit refilling of the container.
In U.S. Pat. No. 2,019,251, a filling spout is provided which, after filling, is covered by a cap that masks the filling spout and can be screwed onto the container but not screwed off. A one-way valve permits exit of fluid from the container but prevents entry of fluid into the container by any route other than that which is exposed in the absence of the cap.
German Patent No. 299,280 discloses a device in which a liquid soluble retainer holds a ball in a raised position long enough to permit filling of the container, after which the retainer dissolves and the ball falls to a position in which the ball will permit only one-way movement of fluid past the ball, that is, the ball permits the discharge of fluid from the container but prevents refilling of the container.
EP 0 008 662 discloses an annular flap valve structure that is deformable to permit filling and emptying of a container but not to permit refilling.
These latter patents have various disadvantages: they may be useful only with a liquid, not a gas; or they require a difficult and time-consuming and expensive assembly; or they require special knowledge or skill of the person who fills the container or who prepares the container for shipment to the customer.